This graph is a visual for you to see your hormone cycle in phases instead of days. The follicular phase is the time when you are on baseline estradiol only, and the time when you may be having a menstrual bleed days 1-5, the new follicles are developing into a dominant follicle that will lead to the ovulatory phase. The ovulatory phase is when the estrogen peaks (due to the dominant follicle) and this then begins the luteal phase when you are now using both estrogen and progesterone. The Cycle day are guideposts so that you know where you are in each phase of the cycle. This graph is representing a 28 day cycle.
Your practitioner may adjust your dose to get your blood levels optimal. Estradiol should cycle between 150-500 pg/ml and progesterone between 1-19 ng/ml in the 28 day cycle. These changes can be made per your prescriber based on physical symptoms and response to the hormones and by monitoring your lab results.